Protective system



Feb. 29, 1944. E. E. MOYER 2,343,399

PRGTZCTIV'LI SYSTES'.

Filed Feb. 24, 1941 Fi I.

LA MIN/(7E0 Inventor: Elmo E. Moaer, b W MMZ His Attorneg.

electro-magnetically operated circuit In- Patented it 1944 position andint-c with the teach ngs will not seal in. due to flux in the reversedirecticn even though the reverse current is o; large magnitude. Thisfeature is of particular 1m portance in connection with the protectionof electric discharge valves from reverse currents due to arc-backs.

It is an object of my invention to provide an improved protectivesystem.

It is a further object of my invention to provide an improved reversecurrent protective systerm.

It is another object of my invention to provide an improved reversecurrent protective system in which reliable operation is assured when areverse current of large magnitude occurs.

It is a still further object of my invention to provide a new andimproved protective system particularly adapted for the protection ofelectric valve converting systems in which the condition ofsubstantially zero operating flux in the magnetic structure of thecircuit interrupter is maintained regardless of the magnitude of thereverse current.

In accordance with the illustrated embodiments, I have shown myinvention applied to a reverse current protective system for an electricvalve rectifier. The contacts of a circuit interrupter are connected inthe anode lead of each of the electric valves of the rectifier circuit.The circuit interrupter is of the type comprising an operatingmechanism'including a magnetic circuit having a movable armature. In theparticular arrangement disclosed the magnetic circuit includes apermanent magnet for producing a the reverse direction moved from 1circuit. My invention v ill Le erence to the following desert I tood byreitaken in conawing and its Jelfitld claims. In the drawing, "Fig. isrepresenta tion oi one embodiment of n1 ition applied to an electricvalve rectifier system and Fig. 2 is a modification of a portion oi thesystem of Fig. 1.

Referring now to the drawing, have shown my invention embodied in aprotective system for an electric valve rectifier for transmittingenergy from an alternating current circuit ill to a direct currentcircuit H and including a supply transformer l2 having a secondarywinding l3 the midpoint of which is connected to one of the directcurrent lines II. The and terminals of the secondary winding H areconnected respectively to the anodes M of electric discharge valves I5and IS. The electric discharge valves may be of any type well known inthe art, and preferably each comprises an envelope containing a gas orvapor and including in addition to the anode M, a cathode H. Thecathodes H of the electric valves l 5 are connected together and to theother side of the direct cugrent circuit if Inasmuch as the presentinvention is equally applicable to rec-- t-ifiers of the controlled anduncontrolled type, control electrodes and circuits for energizing thesame have been omitted to simplify the drawing.

Connected in circuit with the anode of the discharge valves 55 and M arethe contacts 58 of a interrupting device illustrated generally operableclosing switch 3i.

by the numeral 59. Since both or devices 59 are identical, only one hasbeen shown in detail and only one will be described. The interrupterincludes a magnetic circuit comprising a laminated core member 23 ofsubstantially U-shape which is closed in the closed circuit position ofthe contacts l8 by a movable armature 25. A permanent magnet pole facemay be provided on the core 28 or, as illustrated, the member 25 may beformed wholly or partially of permanent magnet material preferably ofthe type having a high coercive force, such as Alnico. The armature 2!is biased to open position by a spring 22. The strength of the permanentmagnet is selected with respect to the spring 22 so that the contacts itare held in closed position when they are once closed, but the fluxproduced thereby when the armature is in open circuit position is notsufiicient to cause the closure thereof. Wound on the magnetic coremember 23 are potential coil sections 23 and 2 having a common terminal25 connected to one terminal of a source of direct current voltage suchas the battery 26. The end terminals of the sections 23 and 24 areconnected to the other terminal of battery 26 through trip and closecircuits, respectively. The trip circuit includes fixed contacts El,current limiting resistor 28 and manually operable tripping switch 29.Similarly, the end terminal of coil section 26 is connected to the otherterminal of battery 23 to fixed contacts 39 and manually The fixedcontacts 271' of the tripping circuit are bridged by a contact member 32in the closed circuit position of the circuit interrupter 95. Asillustrated in the drawing, the member 32 is supported in insulat- 7 edrelation with respect to the armature 2!. A reverse current operatingcoil 33 connected in series with the anode lead of the electric valve 05is wound on the core member 20 in a direction to produce a fiux whichaids the permanent magnet flux in holding the armature 2! in closedposition when the current is flowing through the valve E5 in the normaldirection.

In order to prevent a build-up of flux in the magnetic circuit,including core 20 and armature 2!, in a reverse direction in response toa reverse current of large magnitude and in this way seal-in theinterrupter before the contacts it! have had an opportunity to separate,I provide means associated with the coil sections 23 and 24 for limitingthe flux produced in the core 20 by the reverse current coil 34 to sucha value that the net flux, due to the permanent magnet and the reversecurrent, is substantially zero. In the arrangement shown in Fig. 1 thismeans comprises a resistor 34 and a glow discharge device 35 of the typerequiring a predetermined voltage for producing ionization. Resistor 34and glow discharge device 35 are connected in parallel and across theend terminals of the potential winding sections 23 and 24. Upon theoccurrence of a reverse current in the coil 33, due for example to afailure of the electric valve IS, a voltage will be induced in thewinding sections 23 and 24 having a value dependent upon the rate ofchange of current in the current coil 33 permament magnet flux. lowresistance path across the coil sections 23 and 2t) and an incree in tflux due to reverse current will be prevented. Kr this way the period ofsubstantially zero flux will be maintained independently of themagnitude of the reverse current and the armature M will not have atendency to seal-in and prevent opening of the anode circuit by thecontacts 58. It may be desirable in some cases to provide switch 38'operable to open circuit position when switch 3i is closed to remove thedischarge device from the circuit and prevent it from limiting thepickup flux produced by coil section 2 5. From what has just been saidconcerning the operation of the arrangement of Fig. 1, it is apparentthat this circuit is responsive to the rate of change of reverse currentrather than to an integrated quantity which will indicate when the fluxdue to the reverse current is equal to the permanent magnet flux. Beforedescribing the operation of Fig' l in detail, let us consider themodification shown in Fig. 2 in which means are provided for and theimpedance of the circuit including resistor 34 and device 35. For agiven installation it is possible to design-the reverse current coil andthe coil sections 23 and 24 and to select the constants of the resistor36 and the glow discharge device 35 so that the discharge device willbreak down at substantially the time that the flux due to the reversecurrent is equal to the rendering the response dependent upon the totalchange in current through the current coil so that the circuit willrespond more accurately to limit the flux due to reverse current at theproper time. The modification shown in Fig. 2 is generally similar toFig. l and like numbers have been used to designate the same parts. Inconnection with Fig. 1, it was pointed out that the resistor 34 and glowdischarge device 35 respond to the rate of change of flux in themagnetic cir cuit of the breaker and for this reason do not give anaccurate indication of the time at which the net flux in the core iszero, under varying operating conditions. In the modification shown inFig. 2 means are provided for integrating the change of flux so that anindication of the total flux change may be obtained and in this way theopposing flux may be limited more accurately to a value which produceszero net flux in the core structure.

Referring now to Fig. 2, the coil sections 23 and 24 are shunted by acircuit including in one branch a grid controlled glow discharge device36 having a control grid 37, and a second branch including a resistor 38and a capacitor 39 connected. in series. The common terminal of theresistor 38 and capacitor '39 is connected to the control grid of theglow discharge device through a current limiting resistor M3. Theremainder of the circuit is the same as that described in connectionwith Fig. 1 and the parts thereof have been designated by the samenumerals. Since the voltage across the capacitor 39 is a function notonly of the voltage induced in the coil sections 23 and 24 but also oftime, it is apparent that this arrangement will be responsive not to therate of change of flux in the magnetic core structure alone but to anintegrated quantity of rate of flux Change and time. As a result thetime of breakdown of the glow discharge device 36 more efi'ectivelymaintains the net flux in the magnetic structure at zero value.

A brief description of the operation of the illustrated embodiments ofmy invention will be given although it is believed that in view oftheforegoing detailed description it will be apparent to those skilled inthe art. When operating as a rectifier, the electric discharge valves i5and I6 are efiective to convert alternating current from the circuit itto direct current supplying the circuit i I. The permanent magnetstrength of the circuit interrupter is such that the flux due to thearuiatu e l open position. tions .23 e

connected with t in such direction t produced tripping circu it t fluxdue to the rmagnet and trip the interrupter. while the so n 2d which isconnected in circuit with the o Wery 5 and the clos- Eng switch iiiproduces a flux which assists the permanent magnet flux. i'he flux dueto the current coil 33 is in a direction to aid the holding fluxproduced by the permanent magnet when the current is in the normaldirection. Since the rate of change of flux due to the direct currentpulses of current in the anode circuit may be fairly large, the voltageinduced in the coil winding sections 23 and 24 ma be sufllcient to causethe glow discharge devices 35 or 36 to glow when the valve associatedtherewith is conductive and in this way provide an indicator of normaloperation of the electric valve. If there is reverse current due toarc-back or other failur of the circuit, the flux due to the currentcoil 33 opposes the holding flux and when it becomes equal there- -ientto overcome the to the net flux in the core is zero and the structure iseasily opened under the influence Of the biasing spring 22. In order toprevent scalingin of the armature 2| due to a build-up of flux in thereverse direction due to a reverse current the net flux is maintained ata substantiall zero value by means of the resistor 34 and glow dischargedevice 35 which operate in response to the voltage induced in the coilwinding sections 23 and 24 or in other words to the rate of change influx in the magnetic circuit of the interrupter. The resistor 34 acrossthe coil sections 23 and 24 prevents the voltage of the coil sectionsfrom reaching the breakdown value of the discharge device 35instantaneously. As previously stated, this arrangement is anapproximation ince it responds to the rate of change of flux rather thanto the total change of flux. The arrangement shown in Fig. 2, however,approximates this desired operating condition more closel and in thisarrangement the condenser 38 is charged in response to the voltageinduced in the coil sections 23 and 24 due to the change of flux in thecore structure '20. Since the voltage on the condenser 38 is responsivenot only to the magnitude of the voltage induced in the coil sections 23and 24 but also to time, it is apparent that in this arrangement thetotal voltage on the condenser is a measure of the flux change in thecore structure of the interrupter. Explained in another way, thecapacitor voltage lags the coil voltage approximatel 99 degrees and istherefore more nearly in phase with the coil flux which it is intendedto measure. The voltage of the condenser is utilized to determine thebreakdown of the discharge device 36 and in the particular arrangementis utilized to control the voltage of the control grid 31.

While I have shown and described particular embodiments of my invention,it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention in itsbroader aspects and I, therefore, aim in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A reverse current protective system com responsive to the change offlux in said .ro for tripping and clo rent coil associated aunidirectional therethrough, and means associated v cor for limiting thechange in flux in a structure due to a reversal of current in currentcoil to prevent the due verse current from holding said circuit 1.1Lrupter in closed position.

2. A protective system for an. electric comprising in combination acircuit including a magnetic circuit having a armature associatedtherewith, meal 1 ducing a holding flux in said magnetic c hold saidarmature closed producing a flux in opposition t0 flux in response to areversal of co circuit controlled by said interruptei circuit clue to areversal of current for l g the magnitude of said last mentioned flur;to p.event said armature from being held closed position thereby.

3. A protective system for an electric circuit comprising in combinationa circuit interrupter including a magnetic circuit having a movablearmature associated therewith, means for producing a holding flux insaid magnetic circuit to hold said armature in closed position, meansfor producing a flux in opposition to said hold ing flux in response toa reversal of current in the circuit controlled by said interrupter, andmeans comprising a glow discharge device and means including resistancemeans connected in parallel and associated with said magnetic circuit tobe responsive to the rate of change of flux in said magnetic circuit forlimiting the magnitude of said second named flux to prevent saidarmature from being held in closed position thereby.

4. A protective system for an electric circuit comprising in combinationa circuit interrupter including a magnetic circuit having a movablearmature associated therewith, means for pro ducing a holding flux insaid magnetic circuit to hold said armature in closed position, meansfor producing a flux in opposition to said holding flux in response to areversal of current in the circuit controlled by said interrupter, a.winding associated with said magnetic circuit and having a seriallyconnected resistance means and capacitor connected across the terminalsthereof, electric valve means paralleling said resistance means andcapacitor and having a control member energized in accordance with thevoltage of said capacitor.

5. A protective system comprising in combination, an electric circuit, acircuit interrupter connected to protect said circuit and including amagnetic circuit having a movable armature associated therewith, meansfor producing a holding flux to hold said armature in closed position,a. winding associated with said magnetic circuit for producing a fluxhaving a magnitude dependent upon the current in said electric circuitand wound in a direction to produce a flux opposition to said holdingiiux 1 ice to ing means to produce a a reversai of cmrent in saidelectric circuit, means eiectrmrnagneticaliv associated with saidmagnetic circuit for limiting the flux produced by said reverse currentto prevent said armature from, being held in closed position by saidlast mentioned flux.

6. A protective system comprising in combination, an electric circuit,an interrupter having the contacts thereof connected in said circuit andincluding a magnetic circuit having a movable armature associatedtherewith normally biased to open position, means for producing aholding flux to hold said armature in closed position, winding meansassociaited with said core, means energizing said Winding means toproduce a flux in one direction to overcome said holding flux and allowsaid armature to move to open position, means for energizing saidwindi'iux in the opposite direction to move said armature to closedposition, a winding associated with said magnetic circuit energizedresponse to current of said electric ci cuit, said iast mentionedwinding being Wound in a direction to produce a flux in i: an to saidholding flux when the current in said electric circuit reverses, andmeans as- .lid first entioned winding .x'or iirr'ting he magnitude offlux produced by a rev .cai of current to prevent said armature frombeing iieldvin closed position when said reverse current reaches a largevalue.

'I. A protective system comprising in combination a circuit interrupterincluding a magnetic circuit having a movable armature associatedtherewith, permanent magnet means associated with said circuit forproducing a flux to hold said armature in closed nosition, means forbiasing said armature to open position, said holding flux having amagnitude sufficient to hold said I said magnetic circuit to hold saida1 armature in closed oosition of said biasing means but insufficient toone said armature from open position closed oo sition, winding meansassociated with said magnetic circuit, means for energizing said windingmeans to produce a flux in opposition to said holding flux to open saidcircuit interrupter, means for energizing said winding means in adirection to aid said holding flux to move said armature to closedposition, a Winding asso ciated with said magnetic circuit for producinga fin responsive to the current in said electric circuit and in adirection to oppose said holding flux when the current in said electriccircuit reverses, and means responsive to the product of voltage inducedin said first mentioned windin means and time for limiting the fluxproduced in said magnetic circuit by said last mentioned Winding.

8. A protective system for an electric circuit comprising in combinationa circuit terrupter including contacts said circuit comprising amagnetic circuit having a inovacie armature controliing the movement ofone or said contacts, means for producing a noidir ux in closedposition, a coil associated with and conducting a current dependent uponcurrent of said electric circuit and producing flux in said coreopposing the action or said holding flux when the current in saidcircuit reverses from the normal direction, and means responsive to theproduct of the rate of change of flux and time for limiting the finsproduced in said core structure by reverse current in said coil toprevent said armature from being maintained in closed position by rapidreversal of current in said circuit.

ELMO E. MQYER.

